As a structure of a resin-made pipe joint which is used for a tube for a fluid (for example, high purity liquid, ultrapure water, or chemical liquid) to be handled in a production process of various technical fields such as production of semiconductor devices, production of medical equipment and medicines, food processing, and chemical industry, for example, a structure of a resin-made pipe joint disclosed in Patent Literature 1 is known.
A structure of a resin-made pipe joint of this kind comprises an inner ring (sleeve), a joint body, and a union nut, and is configured so as to be coupled to a tube by connecting one longitudinal (axial) end portion of the tube, to the joint body through the inner ring, and holding the connection state by the union nut.
Here, the inner ring is configured so as to be press-inserted from the one axial side into the one longitudinal end portion of the tube so that the one longitudinal end portion of the tube that is flexible is flared, and the diameter-increased portion is held. The joint body is configured so as to be able to be coupled to the inner ring.
The union nut can be fitted onto the tube so as be relatively movable in the longitudinal direction of the tube, and is configured so as to be fastened to the joint body in order to hold the state where the inner ring which is press-inserted into the one longitudinal end portion of the tube is coupled to the joint body.
Then, the inner ring is configured so as to have a taper-like outer circumferential surface that is formed in such a manner that the outer circumferential surface is flared as advancing from the one axial side toward the other side in order to flare the one longitudinal end portion of the tube, and form a sealing portion which seals between the outer circumferential surface and the inner circumferential surface of the one longitudinal end portion of the tube.
When the structure of a resin-made pipe joint and the tube are coupled together, therefore, the sealing portion is formed, and an edge portion of the union nut which is fastened to the joint body causes a part of the one longitudinal end portion of the tube to butt against the outer circumferential surface of the inner ring, thereby enhancing the sealing property of the sealing portion.
In the case where, when the structure of a resin-made pipe joint is used for the tube, the usage environment is under a high-temperature and high-pressure atmosphere or the period of use is prolonged, however, there is a possibility that the fastening force of the nut may be lowered because of the creep phenomenon, and a sufficient sealing property may not be ensured in the sealing portion. In this case, moreover, there is another possibility that the tube may easily slip off the inner ring.